Question

I like using the is None test for empty variables, it’s very flexible, easy and useful. It seems to have stopped working now:

>"" is None
False

>[] is None
False

>{} is None
False

What’s going on?

I’m using Python 2.6.6 (r266:84292, Dec 27 2010, 00:02:40) [GCC 4.4.5], on Debian/Sid i686 GNU/Linux.

Edit: Awesome tip from Sven Marnach of using bool(“”). brb, off to edit some code…

Answer 1

The test x is None tests if x really is the None object (that is, if the name x references the object None). What you are looking for is truth value testing:

if "":
    print "non-empty"
else:
    print "empty"

if implicitly converts the condition to bool. You can also explicitly do this:

>>> bool("")
False
>>> bool("x")
True